10.2 mtu vs ip mtu command

Hi there,

While doing the QOS 10.2 WFQ section, I configured the serial with the following config :

r4  r5
int s0/1
 clock rate 128000
 bandwidth 128000
 hold-queue 256 out
 tx-ring-limit 1
 mtu 160
 fair-queue 16 128 8

I noticed that the solution configures "ip mtu 156" and not "mtu 160".

Is there a difference between the 2 commands ? Would "mtu 160" be an acceptable solution ?

Cheers